The present invention relates to a mobile communication system; and, more particularly, to an apparatus and method for processing a handover in an international mobile telecommunication-2000 (IMT-2000) system.
An international mobile telecommunication-2000 (IMT-2000) system is developed in order to provide mobility in a worldwide to a subscriber. In the IMT-2000 system, a terminal capable of transmitting various types of data, e.g., a voice signal, a data signal and a paging signal, multimedia and intelligent services are provided and security of personal information is guaranteed of by a personalization of service. The IMT-2000 system accommodates various kinds of terminals, e.g., a cellular phone and a car phone, and various kinds of services, e.g., a global mobile personal communication system (GMPCS), a public switched telephone network (PSTN) and an integrated services digital network (ISDN).
In order to increase an efficiency of limited frequency resources, the mobile communication system divides a whole of service area into small service areas, each of which is referred to a cell, and provides a service based on the cell. At this time, in order to guarantee a mobility of a subscriber, though a mobile station of the subscriber moves out from a service cell, a communication channel between the mobile station and the base station is handed over to another base station, which is referred to a handover. The handover means that a new communication channel is assigned to a mobile station by a base station in a cell to which the mobile station moves, when the mobile station communicating with another mobile station moves from a cell to another cell.
In general, the handover method is divided into two methods, a hard handover method and a soft handover method.
The hard handover method means that the communication channel between the mobile station and the base station communicating therewith is disconnected and then the new communication channel between the mobile station and the base station to be communicated therewith is connected. Using the hard handover, a communication disconnection can occur.
The soft handover method means that the new communication channel is connected before breaking the communication channel between the mobile station and the base station communicating therewith.
Requirements such as a threshold, a probability of a handover fail depend on a kind of telecommunication service. The handover should not fall down an efficiency of a network or a radio resource.
The handover can be performed for changing capabilities of a bearer or security codes necessary for an authentication. The hard handover gives an effect on not continuity or a quality of a service but a security degree; information for the handover should be minimized. The handover should be provided in various sizes of cells, for example, a pico cell, a micro cell, a macro cell and a mega cell.
FIG. 1 is a diagram illustrating a conventional method for processing a handover in the IMT-2000 system.
In the conventional handover method, a handover between mobile switching centers or a handover between networks can occur a serious problem.
Referring to FIG. 1, in a handover model based on a path re-routing method, an old base transceiver station (BTS) transmits a message having an identity of a new BTS to a node. The node searches to an optimum path between the old BTS and a target BTS. If there is the optimum path, the node is selected by a cross over switch, a setup message is generated and a new connection is set. However, if the cell is transmitted before the new path setup, a cell loss, which is a critical problem to a data communication, occurs. Accordingly, in the prior art, a cell buffering function block in the BTS or the MSC solves the above problem.
There are some problems in the conventional optimum handover as follows.
First, a connection setup delay varies depending on environments of a network because of characteristics of a connection-based asynchronous transfer mode (ATM). Accordingly, there is a problem in that it is difficult for a buffer to be enlarged enough. The enlargement of the buffer occurs to waste the resource. Also, the delay from buffering occurs to fall down the quality of a real-time based service.
Second, by using the same algorithm to both of a voice signal and a non-voice signal, the characteristic of the ATM is disregarded. For example, since the voice signal is less sensitive to a delay time, the delay time in the handover is not critical to the voice signal. However, since a high rate data signal is very sensitive to the processing time, the high rate data signal should be handed over within a short time.
Next, a re-routing path selected by the COS cannot be guaranteed as the optimum path, though a capability of accumulation in a quality of service is reduced by reducing a hopping count due to a path re-routing method based on a dynamic COS selection algorithm. It is difficult for a group handover due to the dynamic COS selection to be managed. Accordingly, a multimedia service, which is one of objects of the IMT-2000 service, cannot be provided easily.
As a result, when processing the handover between the MSCs, a variation of network loads becomes a critical obstacle in a rapid handover processing, a cell sequencing and a cell loss compensation.
Therefore, it is an object of the present invention to provide an apparatus and method for rapidly and efficiently processing a handover in an IMT-2000 system.
It is another object of the present invention to an apparatus and method for preventing a resource from being wasted when processing a handover.
In accordance with an aspect of the present invention, there is provided an apparatus for processing a handover in an international mobile telecommunication-2000 (IMT-2000) system, the apparatus comprising: means for performing an interface with a base station controller and an analog subscriber interface for a test; means, having a structure of a non-blocking common memory, for switching an asynchronous transfer mode cell; and means for performing a trunk interface.